Tiscali has blamed spammers for email problems suffered by many of its users for over a week.
Customers have said that emails are not reaching their destinations, and one Tiscali user forum contains over 50 pages of complaints.
Tiscali claims that its email servers have been targeted by spammers, which has resulted in other ISPs blocking email from Tiscali addresses.
"Our engineers are taking urgent action to block the spammers abusing our email service, and this will take effect over the next few days," said a spokesman.
"We will post daily updates on the Service Status page and within forums until normal service is resumed.
"New hardware is being installed and spam filters are being updated. It is likely to take seven to 10 days for these changes to take effect across receiving email providers."
Tiscali is advising affected users to use a free webmail service until the problem has been fully resolved.
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